If a piezoelectric element such as lead zirconate titanate (PZT), quartz (SiO2), or zinc oxide (ZnO) is deformed by an external force, electric polarization is formed in an inner portion of the material, so that positive and negative charges occur on a surface thereof. This phenomenon is called a piezoelectric effect. There have been disclosed power generating methods using this property of the piezoelectric element, where weight is repetitively applied to the piezoelectric element by vibrating a cantilever and charges occurring on the surface of the piezoelectric element are extracted as power.
For example, JP-A-7-107752 discloses a technique where an AC current is generated by vibrating a metal cantilever having a mass installed to a distal end and a thin plate made of a piezoelectric element attached thereto and by extracting positive and negative charges alternately being generated in the piezoelectric element according to the vibration and, after the AC current is rectified by a diode, the current is stored in a capacitor to be extracted as a power. In addition, JP-A-2005-312269 discloses a technique where a contact point is closed only during a time where positive charges are generated by a piezoelectric element, so that a DC current is obtained without occurrence of loss in voltage in a diode. If these techniques are used, a power generation unit can be miniaturized, so that applications such as integration with a small-sized electronic part as a substitute for a battery are expected.